A known image reading apparatus includes a housing, a first guide portion, a second guide portion, and a reader. The housing has a first introduction opening, a second introduction opening, and a discharge opening. A medium is inserted into the first introduction opening. The medium inserted into the first introduction opening is discharged from the discharge opening. A portion of the discharge opening serves as the second introduction opening. The length of the second introduction opening in a width direction is shorter than that of the first introduction opening. A medium having a width smaller than that of the medium to be inserted into the first introduction opening is inserted into the second introduction opening. The medium inserted into the second introduction opening enters into the housing and is then conveyed backwards to discharge from the discharge opening. The first guide portion has a conveyance path through which the medium inserted into the first introduction opening is guided toward the discharge opening. The second guide portion is configured to guide the medium inserted into the second introduction opening to join the conveyance path. The reader is positioned on the side of the discharge opening with respect to a position where the second guide portion joins the conveyance path. The reader is configured to read an image on a medium guided by the first guide portion or the second guide portion.